Granting access to submissions to another user

I added a restriction that only the webform owner can see the submissions.

Now I want that another specific user can access submissions of a specific webform. I added the following code in the beginning of webform_submission_access() but access is not granted:

global $user;
if($user->uid == 4) {
	return true;
}

Is there any other place I should look into? Or what?

Thanks.

P.S.
I give it here hard-coded for simplicity in order to reduce variables. The full code (including reading from an extra table) is used.